U.S. patent application number 16/616553 was filed with the patent office on 2021-06-03 for production of trialkylindium compounds in the presence of carboxylates.
The applicant listed for this patent is Umicore AG & Co. KG. Invention is credited to Angelino DOPPIU, Annika FREY, Ralf KARCH, Andreas RIVAS NASS, Wolf SCHORN, Eileen WOERNER.
Application Number | 20210163502 16/616553 |
Document ID | / |
Family ID | 1000005435682 |
Filed Date | 2021-06-03 |
United States Patent
Application |
20210163502 |
Kind Code |
A1 |
SCHORN; Wolf ; et
al. |
June 3, 2021 |
PRODUCTION OF TRIALKYLINDIUM COMPOUNDS IN THE PRESENCE OF
CARBOXYLATES
Abstract
The invention relates to methods for the production of
trialkylindium (InR.sub.3), wherein the production takes place in a
reaction mixture that contains at least one alkylindium halide, a
trialkylaluminum (AlR.sub.3), a carboxylate, and a solvent, wherein
R is chosen independently of one another from C1-C4 alkyl, and X is
chosen independently of one another from Cl, Br, and I.
Inventors: |
SCHORN; Wolf; (Waldbronn,
DE) ; KARCH; Ralf; (Kleinostheim, DE) ; FREY;
Annika; (Hanau, DE) ; DOPPIU; Angelino;
(Seligenstadt, DE) ; RIVAS NASS; Andreas;
(Bensheim, DE) ; WOERNER; Eileen; (Nidderau,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Umicore AG & Co. KG |
Hanau-Wolfgang |
|
DE |
|
|
Family ID: |
1000005435682 |
Appl. No.: |
16/616553 |
Filed: |
May 25, 2018 |
PCT Filed: |
May 25, 2018 |
PCT NO: |
PCT/EP2018/063820 |
371 Date: |
November 25, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07F 5/00 20130101; C23C
16/18 20130101; H01L 21/0262 20130101 |
International
Class: |
C07F 5/00 20060101
C07F005/00; H01L 21/02 20060101 H01L021/02; C23C 16/18 20060101
C23C016/18 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2017 |
EP |
I 7173318.1 |
Claims
1. Method for producing trialkylindium, wherein the production
takes place in a reaction mixture that contains at least one
alkylindium halide, a trialkylaluminum, a carboxylate, and a
solvent, wherein the alkyl groups are chosen, independently of one
another, from C1-C4 alkyl.
2. Method according to claim 1, wherein the alkylindium halide has
the formula R.sub.aIn.sub.bX.sub.c, wherein R is chosen from C1-C4
alkyl; X is chosen from Cl, Br, and I; and wherein a=1-2, b=1, and
c=1-2.
3. Method according to claim 1, wherein the halide is chloride.
4. Method according to claim 1, wherein the alkyl is methyl or
ethyl.
5. Method according to claim 1, wherein the alkylindium halide is
alkylindium sesquichloride (R.sub.3In.sub.2Cl.sub.3).
6. Method according to claim 1, wherein the carboxylate is the one
carboxylic acid of formula R'COOH, wherein R' is a hydrocarbon
group with 1 to 20 carbon atoms.
7. Method according to claim 6, wherein the carboxylate has the
formula [R'COO].sub.xM, wherein M is chosen from alkali metal and
alkaline earth metal, and x=1 or 2.
8. Method according to claim 1, wherein the carboxylic acid
corresponding to the carboxylate has a boiling point greater than
200.degree. C.
9. Method according to claim 1, wherein the solvent consists of
hydrocarbons and/or has a boiling point greater than 400.degree.
C.
10. Method according to claim 1, wherein the molar ratio of In:Al
in the reaction mixture is between 3:2 and 2:3.
11. Method according to claim 1, wherein the reaction is performed
at a temperature of less than 100.degree. C.
12. Method according to claim 1, wherein the trialkylindium is
separated out from the reaction mixture via sublimation.
13. Method according to claim 1, wherein the reaction comprises the
following steps: (a) providing a mixture which contains the
alkylindium halide, the carboxylate, and the solvent, and (b)
addition of the trialkylaluminum.
14. Method according to claim 1, wherein the yield of
trialkylindium is greater than 80% relative to the quantity of
indium that is used, and/or wherein the trialkylindium has an
oxygen content of less than 2 ppm.
15. Method according to claim 1, wherein the carboxylate is chosen
from the group consisting of 2-ethylhexanoate, n-oetanoate,
sodium-2-ethylhexanoate, or their combinations.
16. Method for producing a semiconductor containing indium and/or a
coating containing indium, comprising the steps: (i) producing
trialkylindium according to the method according to the invention,
and (ii) performing a metallo-organic chemical vapor deposition
(MOCVD), wherein the trialkylindium is used as a precursor compound
for depositing a coating containing indium onto a substrate.
Description
[0001] The invention relates to methods for producing
trialkylindium, wherein the production takes place in a reaction
mixture that contains at least one alkylindium halide, a
trialkylaluminum, a carboxylate, and a solvent, wherein the alkyl
groups on the indium and aluminum are chosen independently of one
another from C1-C4 alkyl; in particular, the invention relates to a
method for producing trialkylindium (InR.sub.3), wherein the
production takes place in a reaction mixture that contains at least
one alkylindium halide, a trialkylaluminum (AlR.sub.3), a
carboxylate, and a solvent, wherein the alkyl groups R on the
indium and aluminum are chosen independently of one another from
C1-C4 alkyl, and the halides of the alkylindium halide are chosen
independently of one another from Cl, Br, and I.
[0002] Trialkylindium compounds--in particular, trimethylindium and
triethylindium--are used in metallo-organic chemical vapor
deposition (MOCVD) as precursor compounds (precursors) for the
production of indium-based layers. The method serves, in
particular, for the production of semiconductors. In the method,
gaseous precursor compounds are directed into a reaction chamber in
which they react among one another or with additional substances,
and the reaction products are deposited onto a substrate.
Trialkylindium compounds are crystalline, sublimable, or liquid,
distillable compounds that are pyrophoric, and thus ignite
spontaneously in the presence of air.
[0003] With the use of trimethylindium as a precursor compound in
MOCVD methods, the problem exists that even slight polar
contaminants--in particular, oxygen, but also nitrogen or
phosphorus--may inactivate ("poison") the products. For
semiconductor applications, even oxygen contamination in the ppm
range is unacceptable. This entails that particular methods for the
production of trimethylindium must be provided in which oxygen and
other contaminants are nearly entirely avoided.
[0004] Classical methods for the production of trialkylindium are
the Grignard reaction of indium, magnesium, and alkyl halides; salt
elimination reactions of indium(III) chloride and methyllithium;
and transmetalation reactions of indium and metal alkyl compounds.
Such methods are generally unsuitable for the production of
trialkylindium for MOCVD process, because trialkylindium cannot be
provided in the necessary purity. This is due to the fact that such
methods require polar solvents such as ether. These have a
relatively high affinity to indium, which leads to complexings and
to the contamination of the product with oxygen compounds.
[0005] In order to solve the problem of such contaminants, in the
prior art, various methods have been proposed that require no
oxygen-containing solvents. WO2014/093419 thus proposes to react a
precursor compound R.sub.3M.sub.2X.sub.3, where R=alkyl and
M=gallium, indium, or thallium, with a reducing agent. In
particular, hydrocarbons are used as solvents. It is thereby
disadvantageous that elementary sodium is used as a reactant.
Sodium is extremely reactive, difficult to handle, and regularly
leads to unwanted secondary reactions. The use of elementary sodium
is hazardous, especially in a mixture with pyrophoric
organometallic compounds, such as alkyl metal educts and products,
and is less suitable for industrial applications. Only methods with
gallium compounds are described in the exemplary embodiments.
However, the reactivity of gallium and indium is very variable in
such reactions, which involve complexes with halogens and alkyl
groups. The yields are low, insofar there are any at all. The yield
is also examined by NMR only in a crude reaction mixture, and thus
without separation of the product. It is therefore unclear whether
the product may be separated at all, let alone in what quantity and
purity.
[0006] US2006/0047132 A1 discloses various methods for producing
organometallic compounds--in particular, based upon gallium,
indium, aluminum, and zinc--from a plurality of precursor
compounds. The method is performed in the presence of tertiary
amines or tertiary phosphines that form adducts with metals, and
are thereby to support the formation of the desired products. It is
thereby disadvantageous that the low-molecular nitrogen- and
phosphorous-containing compounds that are used contaminate the
products, whereby uses of the products for semiconductor
manufacturing by means of MOCVD are precluded. A purification of
the products via sublimation is not possible, or is possible only
to an insufficient extent, because the boiling point of the
low-molecular tertiary amines or phosphines that are used is
relatively low. In example 12 (the sole example in which an indium
alkyl compound is specifically produced), it is, accordingly,
specified that the attempt at the isolation of the product in a
vacuum was unsuccessful. The crude reaction product, which contains
trimethylindium, the amine base adduct, and the solvent, therefore
could be examined only by means of NMR. Such a method is obviously
not usable in practice, or is usable only to a limited extent, if
high purity products without contaminants are required. Moreover,
two theoretical examples 7 and 8 for the production of
trimethylindium are disclosed. It is claimed that a good result
would be expected. This is implausible because the problem of
separation of the trimethylindium from the crude reaction product
that is described in example 12 is not solved. It is therefore not
to be expected that a good yield would be obtained according to the
speculative examples 7 or 8, let alone that a product with the
necessary purity might be obtained. Rather, it is to be expected
that the methods for producing high purity trimethylindium are
unsuitable for MOCVD processes.
[0007] WO2014/099171 describes methods for producing trialkylindium
compounds from indium carboxylates and alkyl aluminum compounds.
The reaction yields of sublimated trimethylindium are, at
approximately 50 to 55%, low. It is also disadvantageous that
low-molecular components, such as isohexane or triacetate, which
lead to a contamination of the product in the sublimation, are
present in the reaction mixtures. In one method variant, the
low-molecular solvent is replaced after the reaction by a
higher-boiling solvent, whereby the method is relatively
involved.
[0008] WO2015/024894 discloses a method for producing
trialkylindium from precursor compounds of the formula
R.sub.3In.sub.2Cl.sub.3, wherein R is an alkyl group having 1 to 4
carbon atoms. The reaction takes place in a multi-stage method in
which a lithium tetraalkylindate is first produced with
alkyllithium, which lithium tetraalkylindate is subsequently
reacted with an indium chloride component. Although the yields are
relatively high, it would, in principle, be desirable to provide a
simpler method. Also, diethyl ether is used in the method, which
may lead to oxygen contamination of the product via the formation
of adducts.
[0009] U.S. Pat. Nos. 5,756,786 and 6,770,769 B2 relate to methods
for the production of trimethylindium from indium trichloride and
trimethylaluminum in the presence of potassium fluoride. The yields
are approximately 56%, and therefore are in need of improvement.
The secondary product, dimethylaluminum fluoride, has a relatively
low boiling point, and therefore, in the purification of the
product in vacuum, occurs as a contaminant. A high excess of
potassium fluoride is used in the method. In general, the handling
of fluorides in industrial processes is problematic, since the
preparation is complicated and cost-intensive. The reaction
residues must also be deactivated in a costly manner, because
portions of the secondary products, such as K[Me.sub.2AlF.sub.2],
exhibit a high reactivity. An additional disadvantage is that the
solid educts, InCl.sub.3 and KF, have polymer structures.
Therefore, they are insoluble or only poorly soluble in the
nonpolar solvent, squalane. Therefore, the reaction must be
performed at relatively high temperatures above 100.degree. C.,
which leads to safety problems in light of the exothermic reaction
and the pyrophoric compounds that are used. In addition to this,
the reaction may be only insufficiently monitored due to the poorly
soluble educts which are present, distributed inhomogeneously as
solids. The method is also relatively inefficient, because a high
(3-fold) molar excess of the aluminum compound, relative to the
indium compound, is necessary. For the cited reasons, the method is
hardly suitable to being applied industrially.
[0010] Overall, a need thus exists for novel, efficient, and simple
methods for producing trialkylindium at high yield and purity.
[0011] It is the aim of the invention to provide a method which
overcomes the disadvantages described above. A method for the
production of trialkylindium shall be provided in which the product
is obtained at a high yield and high purity. In particular, it
should be avoided that unwanted contaminants enter into the product
which have a disadvantageous effect upon subsequent processes, such
as MOCVD applications. In particular, contaminants with oxygen, but
also with nitrogen, phosphorus, or other metals, should be avoided.
It should be possible to perform the method as simply as possible,
and in as few reaction steps as possible. The starting materials
should be as simple as possible and available in large quantities,
and should be as easy to handle as possible. Overall, it should be
possible to perform the method as simply, efficiently, and
cost-effectively as possible.
[0012] Surprisingly, the aim upon which the invention is based is
achieved by a process according to the claims.
[0013] The subject matter of the invention is a method for the
production of trialkylindium, wherein the production takes place in
a reaction mixture that contains at least one alkylindium halide, a
trialkylaluminum, a carboxylate, and a solvent.
[0014] The alkyl groups are chosen independently of one another
from C1-C4 alkyl. The alkyl groups may be linear or branched. It is
thereby especially preferred that the alkyl groups be chosen from
methyl or ethyl. The alkyl group is especially preferably
methyl.
[0015] The educts, alkylindium halide and trialkylaluminum, have
alkyl groups. These may be chosen independently of one another, and
thus be different. However, it is especially preferred that all
alkyl groups in the reaction mixture be identical. This means that
both the alkylindium halide and the trialkylaluminum have the same
alkyl groups, so that a trialkylindium with identical alkyl groups
is obtained. A reaction is especially preferred in which a
methylindium halide and trimethylaluminum are used to produce
trimethylindium. A reaction is likewise preferred in which an
ethylindium halide and triethylaluminum are used to produce
triethylindium.
[0016] The alkylindium halide preferably has a halide that is
chosen from fluoride, chloride, iodide, and bromide. The halide is,
especially preferably, chloride. In such reactions, chloride is
generally preferable, since the corresponding compounds are
available in a relatively simple manner and cost-effectively.
[0017] In a preferred embodiment, the halide is chloride, and/or
the alkyl is methyl. It is especially preferable that the halide be
chloride and the alkyl be methyl. In this embodiment, the invention
relates to a method for producing trimethylindium from a reaction
mixture that contains a methylindium chloride and
trimethylaluminum.
[0018] The reaction mixture contains at least one alkylindium
halide. What is referred to by the generic term, "alkylindium
halide," is a group of compounds of the formula
R.sub.aIn.sub.bX.sub.c that consists of indium, alkyl, and halogen.
The term therefore does not mean that alkyl, indium, and halide are
present in a ratio of 1:1:1. In alkylindium halides, the metal
indium forms, with the alkyl- and halide groups, a metallo-organic
complex or a salt thereof. In general, such metallo-organic indium
halides are often present as a mixture of various compounds that
are at equilibrium with one another. The molar ratios a:b:c of
alkyl, indium, and halide are thereby overall often not whole
numbers, and they may also vary depending upon the concrete
production method. Rather, the compounds are polymers with variable
structures. The concrete structures are thereby in part unknown,
since they have not yet been entirely clarified in the prior art.
According to the invention, however, it is essential that an
organometallic complex be used that has alkyl and halide groups.
The molar ratios may be determined without additional measures via
elementary analysis or NMR tests.
[0019] In a preferred embodiment, the alkylindium halide has the
formula R.sub.aIn.sub.bX.sub.c, wherein R is chosen from C1-C4
alkyl; wherein X is chosen from Cl, Br, and I; and wherein a=1-2,
b=1, and c=1-2. R=methyl or ethyl, and X.dbd.Cl, is thereby
preferred. The molar substance amount ratios of R:In:X may thus
vary between 1:1:2 and 2:1:1. In practice, such alkylindium halides
are also described as mixtures of compounds of the formulas,
R.sub.2InX and RInX.sub.2. In these compounds, the specific
compositions also often vary within the cited ranges, wherein the
specific stoichiometry depends upon the production method.
[0020] In a preferred embodiment, the alkylindium halide is an
alkylindium sesquichloride (R.sub.3In.sub.2Cl.sub.3). The compound
R.sub.3In.sub.2Cl.sub.3 may also be described as an equimolar
mixture of R.sub.2InCl and RInCl.sub.2. In practice, such compounds
normally are not present in precisely the indicated ideal molar
ratio. For example, it has thus been found that the molar ratio of
methyl to chloride in the methylchloride compounds may be at
approximately 2:3. The total formula may thereby be specified as
Me.sub.2,4In.sub.2Cl.sub.3,6.
[0021] Methods for producing alkylindium halides are known in the
prior art. They are often based upon the reaction of indium halides
with alkyl halides. The production of alkylindium sesquichloride is
described in WO2015/024894A1, for example. Additional methods are
disclosed in Gynane et al., J. Organomet. Chem., 40, 1972, C9-C10,
or Gynane et al., J. Organomet. Chem., 81, 1974, 329-334. In U.S.
Pat. No. 5,817,847, the reaction of MeCl with molten indium is
described, wherein MeInCl.sub.2 or Me.sub.2InCl is obtained
(Me=methyl), depending upon the reaction time.
[0022] The reaction mixture has at least one trialkylaluminum,
wherein alkyl is preferably methyl or ethyl. Trialkylaluminum
compounds are organometallic compounds of the general formula
AlR.sub.3. Such compounds are generally present as dimers or
polymers in which each aluminum atom is coordinated more than three
times. In the method according to the invention, trialkylaluminum
serves to provide alkyl groups for reaction with the indium
compound. Overall, in the reaction, alkyl groups transfer from the
aluminum compound to the indium compound. Such methods are also
referred to as transalkylation.
[0023] The reaction mixture has at least one carboxylate. Salts of
carboxylic acid are referred to as carboxylates. Carboxylic acids
are organic compounds that carry one or more carboxyl groups
(--COOH). An ionic compound is thus contained that has at least one
deprotonated carboxyl group. A carboxylate salt is preferably added
to the reaction mixture, which carboxylate salt at least partially
dissociates in the reaction mixture. It is also conceivable to use
a carboxylic acid that is at least partially neutralized in the
reaction mixture.
[0024] According to the invention, it has surprisingly been
established that the production of trialkylindium is markedly more
efficient if a transalkylation is performed in the presence of a
carboxylate. High yields may be achieved in the presence of
carboxylates, wherein high purity products are simultaneously
obtained. The products exhibit no detectable contamination by
oxygen. Moreover, the reaction via the carboxylate is more
efficient, and the quantity of the trialkylaluminum that is used
may be reduced. Without being bound to a theory, it is assumed that
the carboxylate forms, with the educts, intermediary complexes or
reaction products which positively influence the total
reaction.
[0025] The carboxylates are used as further components in addition
to the organometallic indium and aluminum compounds. They are thus
not used as components of organometallic indium and aluminum
compounds, i.e., not as an organometallic indium and aluminum
compound. The method thus differs significantly from that of
WO2014/099171A1, in which indium carboxylates are used as
educts.
[0026] The carboxylates may, for example, have one, two, or more
carboxyl groups per molecule. In a preferred embodiment, the
carboxylate is a monocarboxylate. It has been found that the
reaction with monocarboxylates is markedly more efficient. Without
being bound to a theory, it is assumed that a chelation may occur,
with bivalent or higher-valent carboxylates, that negatively
affects the reaction course.
[0027] In a preferred embodiment, the carboxylate is the one
carboxylic acid of formula R'--COOH, wherein R' is a hydrocarbon
group. The hydrocarbon group may be an alkyl, aryl, or araryl group
having 1 to 20 carbon atoms. The carboxylic acids may be linear or
branched. Such hydrocarbon carboxylates are preferred, since they
are compatible with the reaction mixture and lead to a good
solubility and reaction of the organometallic components. The
solvent is thereby preferably a hydrocarbon. The absence of
additional polar compounds which might negatively affect the
reaction or might contaminate the product is also preferred.
[0028] According to the invention, it has surprisingly been found
that the reaction proceeds very efficiently in the presence of
high-boiling carboxylates. This is advantageous because the
trialkylindium product may be separated via sublimation without
such high-boiling carboxylates entering into the product. In a
preferred embodiment, the carboxylate is therefore the one
carboxylic acid of formula R'--COOH, wherein R' is a hydrocarbon
group that may be an alkyl, aryl, or araryl group and that has at
least 5--preferably, 5 to 20--carbon atoms. The group R' preferably
has 5 to 15--in particular, 5 to 12, and, especially preferably,
7--carbon atoms. The carboxylic acids are thereby especially
preferably alkanoic acids. These may be linear or branched, wherein
branched carboxylic acids are preferred. The carboxylic acids
forming the basis of the carboxylates have relatively high boiling
points that are generally above 200.degree. C. and do not, or only
to a small extent, lead to contaminations of the product purified
via sublimation.
[0029] The carboxylate is preferably the salt of a metal. In a
preferred embodiment, the metal has the oxidation number 1 or 2. In
particular, the metal is an alkali or alkaline earth metal. A salt
of an alkali metal is especially preferably used--in particular, a
sodium or potassium carboxylate.
[0030] The carboxylate is preferably one of the formula
[R'COO].sub.xM, wherein M is chosen from monovalent and bivalent
anions--preferably, metals--and x=1 or 2. In this, x=2, if M is a
bivalent metal. The metals are preferably alkali metals or alkaline
earth metals, since such metals are generally readily soluble and
available. Li, Na, K, Mg, or Ca--in particular, Na or K--are
especially preferred.
[0031] In a preferred embodiment, the carboxylate has the formula
R'--COOM, wherein M is chosen from alkali metal or alkaline earth
metal, wherein R' is a hydrocarbon group having to 6 to 15 carbon
atoms--in particular, 6 to 12 carbon atoms. The carboxylate is
especially preferably a linear or branched octanoate--in
particular, a 2-ethylhexanoate, and, in particular,
sodium-2-ethylhexanoate--or n-octanoate.
[0032] In a preferred embodiment, the carboxylic acid forming the
basis of the carboxylate has a boiling point greater than
200.degree. C.--in particular, greater than 250.degree. C.
Carboxylates with such high boiling points remain in the reaction
mixture upon separation of trialkylindium--in particular,
trimethylindium. For example, octanoic acid has a boiling point of
approximately 237.degree. C.
[0033] The reaction occurs in a solvent. This is selected so that
the educts and the carboxylate may be dissolved as well as
possible, or at least may be suspended. It is thereby preferred
that the solvent be non-polar. In particular, it is preferred that
the solvent have no polar groups, such as oxygen-, nitrogen-, or
phosphorus-containing groups, and/or O, N, or P atoms.
[0034] In a preferred embodiment, the solvent contains
hydrocarbons. It especially preferably consists of hydrocarbons. It
has been found that the reaction may be performed particularly
efficiently in hydrocarbons. The hydrocarbons may thereby be
aliphatic or aromatic hydrocarbons. Alkanes are thereby preferably
used. For example, these may be chosen from pentane, cyclohexane,
decane, heptane, hexane, methylcyclohexane, nonane, octane, or
longer-chained hydrocarbons having 10 to 15 carbon atoms. The
aromatic hydrocarbons may, for example, be chosen from benzene,
toluene, and xylene, or from other mono- or polycyclic aromatics
that may be substituted or unsubstituted. Mixtures of the cited
hydrocarbons may also be used.
[0035] In a preferred embodiment, the solvent consists of
hydrocarbons having a boiling point greater than 200.degree. C.--in
particular, greater than 300.degree. C. or greater than 400.degree.
C. In this embodiment, it is to a great extent advantageous that,
in the purification of the product via sublimation, the solvent not
be or be only slightly distilled, and the product uncontaminated.
It is thereby especially preferred that the solvent have a boiling
point above 400.degree. C. Squalane, which has a boiling point of
450.degree. C., is especially suitable.
[0036] Without being bound to a theory, the method might proceed
according to the following reaction equation (I) if
trimethyldiindium trichloride (methylindium sesquichloride),
trimethylaluminum, and sodium-2-ethylhexanoate are used as starting
materials:
2 Me.sub.3In.sub.2Cl.sub.3+3 Me.sub.3Al+6 Na(2-EH).fwdarw.4
Me.sub.3In+3 MeAl(2-EH).sub.2+6 NaCl (I)
[0037] wherein the sodium-2-ethylhexanoate used as a carboxylate
was shortened to Na(2-EH); with
##STR00001##
[0038] Equation (I) describes an ideal and theoretical reaction. As
was stated above, in practice, alkylindium halides normally exhibit
stoichiometries that, for example, deviate from the ideal ratio of
3:2:3. Moreover, in practice, secondary products such as
carboxylates are obtained in the form of complexes.
[0039] A reaction mixture is provided for performing the reaction.
This contains the alkylindium halide, the trialkylaluminum, a
carboxylate, and a solvent, wherein mixtures of these components
may respectively also be used. The solvent is preferably chosen so
that the educts present therein are distributed as homogeneously as
possible--preferably, as a solution or at least as a dispersion
that is as fine as possible. The mixture of the starting materials
thereby takes place so that as efficient a reaction as possible
takes place, and secondary reactions are avoided--in particular, at
the beginning of the reaction.
[0040] It is an advantage of the method that the reaction proceeds
very efficiently. This leads to the situation that only a
relatively small quantity of the trialkylaluminum must be used,
which, overall, leads to a significant savings of costs. For
example, according to the reaction equation indicated above, only 3
mol aluminum are required for the conversion of 4 mol indium. By
contrast, a relatively high excess of aluminum is often required in
conventional methods. However, according to the invention, it may
be advantageous to use an excess of the aluminum compound in order
to improve the yields. In a preferred embodiment, the molar ratio
of indium and aluminum in the reaction mixture is between 3:2 and
1:2--in particular, between 3:2 and 2:3. The molar ratio between
3:2 and 1:1--in particular, between 4:3 and 1:1--is especially
preferred. It is generally preferred that, in the molar ratio, the
reaction mixture contain more indium than aluminum.
[0041] It is generally preferred to use a molar excess of
carboxylate relative to the indium in order to improve the yields.
The molar ratio of the carboxylate to indium in the reaction
mixture may, for example, be between 1:1 and 5:1--in particular,
between 2:1 and 4:1, and, especially preferably, between 3:2 and
3:1. This is generally non-critical for efficiency reasons, since
carboxylate salts are readily and cost-effectively available.
[0042] The reaction may be performed at a temperature of 25.degree.
C. to 200.degree. C., for example. However, it is preferred that
the reaction be performed at a temperature below 100.degree. C.--in
particular, below 80.degree. C. or below 70.degree. C. The reaction
is preferably performed at a temperature in a range of 25.degree.
C. to 100.degree. C.--in particular, in a range of 30.degree. C. to
80.degree. C. or of 50.degree. C. to 70.degree. C. According to the
invention, it has been found that a very high yield may be achieved
even at a temperature of approximately 60.degree. C.
[0043] It is highly advantageous that, according to the invention,
an efficient reaction occurs even at such relatively low
temperatures. On the one hand, the organometallic compounds used
based upon indium are generally thermally labile. Trimethylindium
thus tends to decompose exothermally above 120.degree. C. and under
development of high pressure. Therefore, for the product yield and
the product quality, it is advantageous that the method may be
performed at relatively low temperatures. On the other hand, both
the organometallic compounds that are used and those to be produced
are generally pyrophoric. Therefore, the hazard potential,
specifically in the case of application on an industrial scale, may
be significantly decreased by setting a low reaction
temperature.
[0044] The reaction is performed over a period of time, until the
educts have entirely or largely reacted. For example, the reaction
may be performed over a time period of 20 min to 20 h--in
particular, between 30 min and 8 h, or between 30 min and 4 h.
Since the reaction proceeds relatively efficiently, reaction times
of less than 5 h or less than 3 h may be sufficient.
[0045] The reaction preferably takes place under strict exclusion
of air and water. Otherwise, unwanted secondary reactions would
occur, because the product, trialkylindium, and also the educt,
trialkylaluminum, are very pyrophoric.
[0046] The reaction into trialkylindium preferably takes place
after mixing all starting materials in a single step, and thus
without needing to isolate the intermediates, or without additional
reactive compounds such as lithium compounds being added
subsequently.
[0047] The trialkylindium is preferably separated after the end of
the reaction. In a preferred embodiment, the trialkylindium is
separated via sublimation. The sublimation preferably takes place
in a vacuum and at increased temperature--for example, at
100.degree. C. to 200.degree. C. According to known methods, the
solid trialkylindium is obtained as a sublimate in a cooled range.
In general, the purified trialkylindium may be further purified
according to typical methods--for example, via drying or
re-sublimation.
[0048] The educts may be mixed in arbitrary order. In a preferred
embodiment, the reaction comprises the following steps: [0049] (a)
providing a mixture which contains the alkylindium halide, the
carboxylate, and the solvent, followed by [0050] (b) addition of
the trialkylaluminum.
[0051] It has been found that the reaction proceeds especially
efficiently if the trialkylaluminum is added last. It is thereby
preferred to add trialkylaluminum in a controlled manner over a
longer period of time--for example, by drops. The speed of the
addition is adjusted so that the reaction proceeds, overall, in a
controlled manner. The trialkylaluminum may preferably react
continuously, and does not accumulate in the reaction mixture. In
particular, the reaction is adjusted so that the temperature
remains constant during the addition of the trialkylaluminum. For
example, the addition of the trimethylaluminum may take place over
a time period of 30 min to 5 h--in particular, between 30 min and 3
h. It has been found that secondary reactions may be avoided in
such a reaction course, and that the yield is especially high.
[0052] In a further embodiment, the reaction comprises the
following steps: [0053] (a1) providing a mixture which contains the
trialkylaluminum, the carboxylate, and the solvent, followed by
[0054] (b1) addition of the alkylindium halide.
[0055] It is thereby preferred that alkylindium halide be added in
a controlled manner over a longer period of time, e.g., by drops,
analogously to the method described above with steps (a) and (b).
In this method control, the fact that alkylindium halides often
have relatively low melting points, and therefore may also be added
in liquid form, is made use of. The methylindium chloride used in
the exemplary embodiments thus has a melting point of approximately
130.degree. C., for example, and could be added by drops in liquid
form. This is an additional advantage compared to the use of
InCl.sub.3 according to the prior art, which possesses a markedly
higher melting point.
[0056] After steps (a) and (b), or (al) and (b1), step (c) of the
purification of the trialkylindium preferably takes place via
sublimation.
[0057] The alkylindium halide in isolated form may be used in the
reaction. It is also possible to produce the alkylindium halide in
a preceding step. The alkylindium halide may either be purified in
an additional intermediate step, or the additional conversion to
trialkylindium occur in the same reaction vessel. For example, the
alkylindium halide--such as an alkylindium sesquichloride--may be
produced via reaction of elementary indium with alkyl halides at
increased pressure and a temperature of 150 to 200.degree. C. The
reaction product produced in such a manner may be mixed directly
with the carboxylate and, if applicable, the solvent, followed by
the addition of trialkylaluminum, whereby the reaction into
trialkylindium begins. It is thereby conceivable to produce
alkylindium halide even in the solvent required for the additional
reaction.
[0058] In a preferred embodiment, the reaction mixture contains no
components, i.e., educts, carboxylates, and solvents, that have a
boiling point below 200.degree. C.--preferably, below 250.degree.
C. or below 300.degree. C. This is especially advantageous, because
such high-boiling compounds are not carried off, or are carried off
only to an extremely small degree, in the final sublimation of the
trialkylindium.
[0059] In a preferred embodiment, no additional compounds are
contained in the reaction mixture apart from the alkylindium
halide, trialkylaluminum, carboxylate, and solvent. In a further
embodiment, the reaction mixture may contain additives.
[0060] In further embodiments, no compound (apart from the inert
gas) that contains nitrogen or phosphorus--in particular, no amines
or phosphines--is added to the reaction mixture. Aside from
carboxylates, preferably, no additional compound that contains
oxygen is added. Preferably, no compound is added that is chosen
from elementary metals and metal halides--in particular, indium
trihalide or aluminum halides.
[0061] In a preferred embodiment, the yield of trialkylindium is
greater than 80% in relation to the quantity of indium used. The
yield is especially preferably greater than 85%, greater than 90%,
or at least 95%. The yield relates, in particular, to the quantity
of trialkylindium after the sublimation from the reaction mixture.
Such high yields in the production of trialkylindium are atypical,
and, in general, are not achieved with conventional reactions.
[0062] The purity of the trialkylindium that is obtained in the
method is preferably at least 99.99 wt %--in particular, at least
99.999 wt %, and, especially preferably, at least 99.9999 wt %. It
has been found that such extraordinarily pure products can be
obtained with the method. The purity preferably relates even to the
product that is obtained directly via sublimation from the reaction
mixture.
[0063] The trialkylindium preferably has an oxygen content of less
than 2 ppm--preferably, less than 1 ppm, and, especially
preferably, less than 0.5 ppm. Such low oxygen fractions are
acceptable in MOCVD applications. The trialkylindium produced
according to the method thus has an extraordinarily low proportion
of oxygen. This was unexpected, because carboxylates are, in
principle, an oxygen source, and it could not be assumed that
nearly no residues from these would get into the product. According
to the invention, it has been found that the oxygen contaminations
are so slight that they cannot be detected by means of .sup.1H-NMR.
The detection limit of this method is approximately 2 ppm.
[0064] The highly pure trialkylindium which can be obtained
according to the method is suitable, in particular, for use as a
precursor compound in the metallo-organic chemical vapor deposition
(MOCVD) for deposition of indium-containing layers. In this method,
it is used, in particular, in gaseous form, wherein a chemical
reaction occurs in the gas phase or on a substrate, and indium
and/or an indium compound is deposited. It is thereby extremely
advantageous that the trialkylindium has no detectable oxygen
contaminants.
[0065] The subject matter of the invention is also a method for
producing a semiconductor containing indium and/or a coating
containing indium, comprising the steps: [0066] (i) producing
trialkylindium according to the method according to the invention,
and [0067] (ii) performing a metallo-organic chemical vapor
deposition (MOCVD), wherein the trialkylindium is used as a
precursor compound for depositing a coating containing indium onto
a substrate.
[0068] The method according to the invention achieves the described
aim, in contrast to the prior art. A new method for the production
of trialkylindium is provided in which the product may be obtained
at a high yield of well above 90%. The method is therefore highly
efficient and cost-effective. According to the invention, a product
of extraordinarily high purity is also obtained in which oxygen
contaminants are not detectable. The product is therefore highly
suitable as a precursor compound in CVD processes for the
production of semiconductors containing indium.
[0069] The method also has numerous advantages with regard to the
method control. It can be performed in a single reaction mixture
and a single reaction step, and therefore is comparatively simple.
A relatively small quantity of trialkylaluminum may be used in
relation to the alkylindium halide that is used as an educt. The
molar ratio of indium to aluminum may thereby be less than 1, or
even lower. On the whole, the quantity of organometallic compounds
used that are pyrophoric and difficult to handle may thereby be
kept small. This is advantageous for both reasons of cost and
hazard prevention.
[0070] The advantages are achieved because carboxylates are used
that are relatively readily available and handled easily. Overall,
a markedly improved and simplified method is provided for the
production of trialkylindium.
[0071] It is an additional advantage that the method may be
performed exclusively with compounds, but also with secondary
products, that have relatively high boiling points above
200.degree. C. It is thereby ensured that a highly pure product is
obtained in the final separation of the trialkyl indium via
sublimation.
EXEMPLARY EMBODIMENTS
EXAMPLE 1
[0072] Methylindium chloride of the formula
Me.sub.2,4In.sub.2Cl.sub.3,6 (referred to in the following as MIC,
produced according to WO2015/024894A1, Example 1.4) was converted
into trialkylindium in an inert gas glovebox. The reaction takes
place in a 1 L three-necked bottle with tempering jacket. 89.9 g
MIC (468 mmol in relation to indium) and 135.5 g
sodium-2-ethylhexanoate (815 mmol) are added to 400 mL squalane and
stirred vigorously with a KPG stirrer. The mixture is heated via
the tempering jacket with a thermocryostat to 60.degree. C.
(external temperature control). 29.9 g trimethylaluminum (415 mmol)
are added by drops via a dropping funnel at a speed [such] that the
temperature remains constant at 60.degree. C. (.+-.2.degree. C.)
(approximately 2 h). After the end of the addition, the dropping
funnel is exchanged for a cooler with cooling fingers, and the sump
is heated to 120.degree. C. The cooler, together with cooling
fingers, is cooled to -25.degree. C., and TMI (trimethylindium) is
sublimated out of the reaction mixture via application of vacuum.
As a sublimate, 70.8 g TMI (443 mmol) are thereby obtained as a
crystalline solid (95% yield). No oxygen-based contamination can be
identified via .sup.1H-NMR.
EXAMPLE 2
[0073] Methylindium chloride of the formula
Me.sub.2,4In.sub.2Cl.sub.3,6 (according to Example 1) was converted
into trialkylindium in an inert gas glovebox. In a 1 L three-necked
flask with tempering jacket, 112.5 g methylindium chloride (587
mmol in relation to indium) and 168.7 g sodium-2-ethylhexanoate
(1,015 mmol) are added to 500 g dibenzyltoluene (market name,
Marlotherm SH, Sasol company, Germany) as a solvent and stirred
with a KPG stirrer. The mixture is heated via the tempering jacket
with a thermocryostat to 60.degree. C. (external temperature
control). 36.9 g trimethylaluminum (512 mmol) are added by drops
via a dropping funnel at a speed [such] that the temperature
remains constant at 60.degree. C. (.+-.2.degree. C.) (approximately
1 h). After the end of the addition, the dropping funnel is
exchanged for a cooler with cooling fingers, and the sump is heated
to 120.degree. C. The cooler, together with cooling fingers, is
cooled to -25.degree. C., and TMI (trimethylindium) is sublimated
out of the reaction mixture via application of vacuum. As a
sublimate, 83.0 g TMI (519 mmol) are thereby obtained as a
crystalline solid (88%). No oxygen-based contamination can be
identified via .sup.1H-NMR.
* * * * *